What absorbs at 2170 cm⁻¹ in an FTIR spectrum?
A band near 2170 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Quick answer
A band near 2170 cm⁻¹ is usually interpreted by checking which functional groups repeatedly co-occur there in the literature, then confirming at least one or two additional peaks in the same sample. This page ranks those assignments by accumulated evidence rather than by a single fixed textbook rule.
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| C#c | 2 | 2 | 1.0 |
| Silicon hydride | 2 | 2 | 1.0 |
| Silicon (Si) | 2 | 2 | 1.0 |
| Adsorbed carbon monoxide | 2 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Bronsted acid site | 1 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Nitrile | 1 | 0 | 1.0 |
| N-O bond | 1 | 0 | 1.0 |
| Water (H2O) | 1 | 0 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| Silica | 2170, 1100, 1080 | Silicon (Si), Hydroxyl (O-H) | 1 |
| Al2O3 | 2170, 1722, 1383 | Hydroxyl (O-H), Silicon (Si) | 1 |
| TiO2 nanoparticles | 2170, 1700, 455 | Hydroxyl (O-H) | 1 |
| MCM-41 | 2170, 1655, 1695 | Hydroxyl (O-H), Silicon (Si) | 1 |
| zeolite | 2170, 1013, 1245 | Hydroxyl (O-H), Silicon (Si) | 1 |
Materials are shown only when the same literature pool supports this band and at least one additional characteristic peak.
Spectrum logic
This band becomes meaningful only when read with its neighboring peaks. In practice, analysts first look at the assignments above, then check whether the same sample also shows other peaks expected for the same structural motif. A lone band near 2170 cm⁻¹ is usually not enough for material identification by itself.
Real-world usage
This type of query is common in polymer identification, unknown plastic screening, QC troubleshooting, recycled-material verification, and literature-backed peak assignment review.
Common mistakes
- Treating one isolated band as proof of a material without checking at least one or two supporting peaks.
- Ignoring overlap: multiple functional groups can contribute near the same wavenumber.
- Skipping validation when additives, blends, oxidation, or contamination may distort the spectrum.
Verification advice
When ambiguity remains, validate the hypothesis with DSC, GC-MS, or TGA, especially for blends, degraded samples, and filled polymers.
Literature behind these assignments
-
confidence 1.0
“3000to form N The peak at 2170 attributwhich a broad band absorption shows in the range of 3-Ti(a) cm-1 V able to HN with the weakest intensity is consistent with 3800 and three sharp peaks related to a(NNN) vibrations 3-Ti(a) cm-1.”
Wang 等 - 2005 - Reactions of hydrazoic acid on TiO2 nanoparticles DOI: 10.1021/jp0458046 -
Hydroxyl (O-H) confidence 1.0
“(v cm(cid:3)1 3280 (OH stretching region) and a CO (CO)) stretching cm(cid:3)1 vibration at around 2170 (CO stretching region).”
Batool 等 - 2022 - Correlating Lewis acid activity to extra-framework DOI: 10.3929/ethz-b-000536201 -
Amide confidence 1.0
“The absence of bands around 2170 which correspond to the stretching of C-N bonds, and can being associated with the presence of adsorbed cyanide as a product of decarboxylation [16, 62], indicates that the process does not involve a”
Gisbert-Gonzalez 等 - 2021 - Glutamate adsorption on the Au(111) surface at dif DOI: 10.1016/j.jelechem.2020.114870 -
C#c confidence 1.0
“LLM confirmed rule peak-group candidate”
Atmospheric Pressure Plasma Polymerized 2-Ethyl-2-oxazoline Based Thin Films for Biomedical Purposes DOI: 10.3390/polym12112679 -
Acetate confidence 1.0
“At low CO coverage, the C-O stretching cm-1 region reveals a signal centered at 2170 corresponding to the stretching mode of CO interacting with Brønsted acid sites.”
Miletto 等 - 2017 - Mesoporous Silica Scaffolds as Precursor to Drive DOI: 10.1002/chem.201701978 -
Silicon (Si) confidence 1.0
“The Si-C stretching is observed at 760 and the peaks at 2170 and cm-1 890 are attributed to the absorption and bending frequencies of Si-H group.”
Nwankire 等 - 2011 - Enhancing the Mechanical Properties of Superhydrop DOI: 10.1002/ppap.201000069 -
Adsorbed carbon monoxide confidence 1.0
“bands at 2170 and attributed to CO adsorbed on Fortheon-topCOconfiguration,theC-Ostretchingfrequencies cationic Pd species (+1 and +2 respectively) probably combined”
Piqueras 等 - 2008 - Pd-gamma Al2O3 applied to triglycerides hydrogenat DOI: 10.1016/j.apcata.2008.05.029 -
C#c confidence 1.0
“LLM confirmed rule peak-group candidate”
Atmospheric Pressure Plasma Polymerized Oxazoline-Based Thin Films—Antibacterial Properties and Cytocompatibility Performance DOI: 10.3390/polym11122069
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